Time-resolved detection of light-induced conformational changes of heliorhodopsin

Heliorhodopsins (HeRs) are a new category of rhodopsins. They exist as a dimer and exhibit a characteristic inverted topology. HeRs bind all-trans-retinal as a chromophore in the dark, and its isomerization to the 13-cis form by light illumination leads to a photocyclic reaction involving several photo-intermediates: K, L, M, and O. In this study, the kinetics of conformational changes of HeR from Thermoplasmatales archaeon SG8-52-1 (TaHeR) were studied by the transient grating (TG) and circular dichroism (CD) methods. The TG method reveals that the diffusion coefficient (D) does not change until the O formation suggesting no significant conformation change at the surface of the protein during the early steps of the reaction. Subsequently, D decreases upon the O formation. Although two time constants (202 mu s and 2.6 ms) are observed for the conversion from the M to O by the absorption detection, D decreases only at the first step (202 mu s). Light-induced unfolding of helical structure is detected by the CD method. To examine the contribution of a characteristic helix in the intracellular loop 1 (ICL1 helix), Tyr93 on the ICL1 helix was replaced by Gly (Y93G), and the reaction of this mutant was also investigated. It was found that this replacement partially suppresses the D-change, although the CD-change is almost the same as that of the wild type. These results are interpreted in terms of different sensitivities of TG and CD methods, that is, D is sensitive to the structure of the solvent-exposed surface and selectively observes the conformational change in the ICL1 region. It is suggested that the structure of hydrophilic residues in the ICL1 helix is changed during this process

Asymmetric interspecific territorial competition over food resources amongst Lake Malawi cichlid fishes

The rock-dwelling cichlids in Lake Malawi comprise the most diverse freshwater fish community in the world. Individuals frequently interact with heterospecifics through feeding territoriality. Underwater observations and experiments were conducted to examine interspecific variation in the frequencies of territorial behaviour and its influence on the feeding habits of heterospecifics. Frequencies of chasing and fleeing associated with interspecific territoriality were remarkably different amongst 10 cichlid species. In addition, individual fish that attacked heterospecifics more frequently were attacked less often by them, suggesting that interspecific interactions amongst cichlid species are asymmetric. The experimental removal of territory owners belonging to the most aggressive species resulted in almost fivefold increase in feeding within territories, suggesting that territorial aggression preserves food resources for the territory holder and influences the feeding habits of other species, including those with some dietary dissimilarities. Additional information regarding asymmetric interspecific interactionswould improve understanding about how diverse cichlids within trophic groups manage to coexist.African Zoology 45(1): 24–31 (April 2010

Relationship between Local and Scientific Names of Fishes in Lake Malawi/Nyasa

An interview survey was carried out in 20 Malawian lakeside villages from 1999 to 2000 to clarify the relationship between local and scientific names of the fishes in Lake Malawi/Nyasa. Fishermen in various localities responded with 536 local fish names for photographs shown of 106 fish species and color morphs. Similarity analysis of local name usage produced three groups of localities corresponding with the Tonga, Tumbuka, and Nyanja/Yao languages. A single scientific fish species had 10.2 local fish names, while one local fish name covered 2.0 scientific fish species, and 64.3 % of local fish names were used only for one scientific species. A few local fish names were used widely irrespective of language, although 69.5 % of local fish names were collected only from one locality. These facts suggest that lakeside residents identify fish at the biological taxonomy level, although the naming was specific to a particular locality. Most fishes with a high variety of local names were shallow-water dwelling species with low local market values, whereas fishes with fewer local names were mainly offshore species of high commercial value

Asymmetric interspecific territorial competition over food resources amongst lake malawi cichlid fishes

The rock-dwelling cichlids in Lake Malawi comprise the most diverse freshwater fish community in the world, Individuals frequently interact with heterospecifics through feeding territoriality. Underwater observations and experiments were conducted to examine interspecific variation in the frequencies of territorial behaviour and its influence on the feeding habits of heterospecifics. Frequencies of chasing and fleeing associated with interspecific territoriality were remarkably different amongst 10 cichlid species. In addition, individual fish that attacked heterospecifics more frequently were attacked less often by them, suggesting that interspecific interactions amongst cichlid species are asymmetric, The experimental removal of territory owners belonging to the most aggressive species resulted in almost fivefold increase in feeding within territories, suggesting that territorial aggression preserves food resources for the territory holder and influences the feeding habits of other species, including those with some dietary dissimilarities. Additional information regarding asymmetric interspecific interactions would improve understanding about how diverse cichlids within trophic groups manage to coexist